One alarm goes off in response to sound, one goes off in response to light, and one goes off in response to vibration.
There are three buttons that each produce one of those effects.
You need to set off all three alarms by pressing the least number of buttons possible.
Select all of the buttons that need to be pressed.
You don't need to press all of the buttons.
An alarm will go off if any of the three buttons are pressed.
This means you don't need to press the button that makes a sound inside the chest.
The only way to get the light alarm to go off is by making it light inside the chest.
Sound is the vibration of air.
That means that there is no need to shake the chest, because if any of the alarms go off, the chest will vibrate.
Answer for 'Cause for Alarm'
The answer is 'Make it light inside the chest'.